Multiple matrix magnetic separators typically use an annular electromagnetic coil or group of coils to provide a magnetic field volume in the space encompassed by the electromagnetic coils. There is a plurality of magnetic matrices arranged in a stacked array in a container within the space encompassed by the electromagnetic coil. Each magnetic matrix generally includes ferromagnetic material such as steel wool or expanded metal enclosed in the container which may be made of stainless steel or other material of low magnetic permeability. The electromagnetic coil, matrices and container may be enclosed in a ferromagnetic return frame to increase the efficiency of the magnetic circuit. The technique of stacking magnetic matrices adjacent to each other to achieve a predetermined matrix area instead of using a single matrix in the same area is employed to reduce the volume of the ferromagnetic return frame surrounding the coil and thereby reduce the cost of the device, a significant portion of which cost is constituted by the cost of the ferromagnetic return frame. Each additional layer used in the stack to accomplish a particular area requirement reduces the diameter of the top and bottom portions of the return frame, the intermediate cylindrical portion, and the electromagnetic coil and increases the length of the coil and cylindrical portion of the frame in the longitudinal direction of slurry flow through the matrices. The number of matrices used to accomplish a particular process capacity is optimized for maximum efficiency.
Typically the feed is submitted to the feed area on one side of each matrix and the separation product or products are recovered from the collection area on the opposite side of each matrix. All matrices have their feed areas facing in one direction and their collection areas facing in the opposite direction. Thus in the stack the feed area of one matrix is immediately adjacent the collection area of an adjacent matrix. Some means is provided between each pair of adjacent matrices in order to ensure that there is no leakage between these two areas. Often a partition is used which is sealed to the container at the periphery of the partition. Practical and useful seals may be accomplished when such machines are small e.g. six or eight inches in width or diameter. However, when the machines are of production size 30 inches, 100 inches or even more in width or diameter such peripheral or circumferential seals are extremely difficult to install and maintain. Yet these seals must be maintained with the utmost integrity for a leak in this area can substantially decrease the efficiency and economy of operation of the multiple matrix magnetic separator: the leak from the feed area of one matrix to the collection area of the next matrix contaminates the separation products at the output with the unseparated feed at the input.